This invention relates to a sensor for a vehicle seat belt retractor. More specifically, the present invention relates to a sensor that reduces or eliminates nuisance locks of seat belt retractors.
In order to provide enhanced comfort and convenience, seat belt retractors employ a mechanism to allow the belt webbing to be freely extended and retracted from the retractor as the vehicle occupant moves in the seat. Of course, in order to provide its occupant protection function, the retractor must lock to prevent webbing pullout as the occupant loads the belt in an impact condition. Most vehicles incorporating such so called emergency locking retractors employ a pendulum or roll ball type inertia sensor in the retractor.
Sensor strategies employed in primary occupant restraint applications must be capable of sensing low “g” or vehicle tilt angles generated during sudden vehicle braking conditions or vehicle roll over events. Sensing these vehicle conditions reliably is paramount to properly restraining the occupant within the seat.
Ideally, a common use retractor sensor design is the preferred choice when used in high volume automotive applications; however, vehicle types and road conditions generally cause the sensor to sacrifice comfort to the occupant in order to achieve FMVSS compliance. A common use design may not be suitable for all vehicles since some vehicles are stiffer or more dynamic than others depending on the road conditions. SUV's and both heavy and light trucks, for example, are more sensitive to conditions of the road, resulting in the vehicle becoming more dynamic in comparison to a small or luxury car (i.e., the vehicle experiences higher pitch, roll, and jounce accelerations in normal driving conditions). Moreover, the position in the vehicle at which the retractor mounted may influence the performance of the sensor. For instance, a retractor mounted low in the vehicle is less sensitive to some of the aforementioned accelerations than a retractor mounted high in the vehicle. Thus, the dynamics of the vehicle, the mounting location of the retractor, and FMVSS performance requirements all directly influence the sensitivity and performance of a common use retractor inertia sensor.
Generally, as the vehicle becomes more subject to road induced accelerations, so does the sensor, creating occupant restraint comfort issues. Such vehicles and common use sensors typically generate hypersensitive retractors, resulting in a repetitive locking and unlocking of the primary restraint, an event commonly referred to as a retractor nuisance lock. Nuisance locks often cause the primary restraint/belts to bite/cinch down on the occupant, restricting occupant movement and causing discomfort to the occupant. Locking of the retractor in response to non-impact or non-rollover events is undesirable as it is an annoyance to the occupants.
Primary restraint sensors must be capable of sensing accelerations/forces in three-dimensional space, such as the space defined by the Cartesian axes X,Y,Z, in order to comply with FMVSS requirements. Such sensors have the ability to detect and communicate the presence of potential adverse frontal, rear, side, roll, braking or combinations of any of the aforementioned vehicle conditions. However, most nuisance locking conditions are generated by a sensor's inability to eliminate or reduce the influence of undesired sensitivity along the “Z” (or vertical) direction. For example, bumps in the road cause the sensor mass to bounce in the “Z” direction, potentially causing the retractor to lock/limit belt displacement. Most often these potential locking conditions result in the retractor to lock, resulting in a nuisance lock and discomfort to the occupant being restrained.
Many primary occupant restraint sensors employ a standing mass or ball excitation mass in combination with a housing and pivot arm to sense adverse vehicle conditions. These sensors often attempt to manage nuisance-locking conditions by changing the mass, the incline angle in which the mass rests, the distance between the inertia lever-arm and the locking mechanics of the retractor, or combinations of the aforementioned features. Unfortunately, when these critical characteristics are modified, the sensor is likely to become unique to a restraint/retractor, an application, an installation or a specific vehicle. The common use sensor, therefore, becomes less suited for diverse applications and is not well suited for the high volume, low cost demands of the automotive industry. Changes such as those mentioned also have the potential of making the sensor become less sensitive and even non-compliant with ECE or FMVSS regulatory performance requirements.